1. Field of Invention
The present invention relates to a coordinate input system for imparting a digitizer function, i.e., a positional coordinate input function to a transmissive screen for image display such as a rear projection display apparatus, and a display apparatus using such a coordinate input system.
2. Description of Related Art
Recent diffusion of personal computers and projecting display apparatuses using a liquid crystal, a light bulb or a CRT is bringing about a common practice of presentation of electronic image information in the form of an enlarged projected image. If a positional instructing operation can be carried out directly on an image displaying screen, the presenter could operate a computer without leaving the screen position, and it would be possible to enter handwritten characters directly onto the screen, thus permitting an effective and efficient presentation. There are therefore developed methods for positional coordinate input on a screen.
An example of such methods for positional coordinate input on a transmissive screen for image display is the one disclosed in Japanese Unexamined Patent Publication No. 60-230,228. This method has a configuration as shown in FIG. 16. In this method, positional coordinates of a light emitting indicator 101 such as a light pen is determined by detecting an invisible ray spot such as an infrared ray spot projected from the light emitting indicator by means of a positional detector 103 such as a Position Sensitive Light Detector (PSD) provided behind a transmissive screen 102, together with a projecting tube 104 which is an image projector forming an image from an image ray onto the transmissive screen 102.
However, the light emitting indicator 101 such as a light pen must have a light emitting diode (LED) serving as a light source, a control circuit and a cell incorporated therein, leading to a larger size and a heavier weight. This method therefore has a problem in that, when an operator enters a positional instruction or handwritten characters onto the transmissive screen 102 with the light emitting indicator 101 in hand, handling is more difficult than in handling writing means such as a pen.
The present invention has therefore an object to achieve a coordinate input system easy to handle on a transmissive screen and a display apparatus provided with such a coordinate input system.
(1) The coordinate input system of the present invention, imparting a coordinate input function to a transmissive screen which forms an image from an image ray projected by image ray projecting means, comprising: infrared ray projecting means which projects infrared ray to a back of the transmissive screen; image sensing means which picks up the infrared ray reflected by indicating means provided with reflecting means in front of the transmissive screen, from the back of the transmissive screen; and image information processing means which determines coordinates on the transmissive screen as specified by the instructing means from an output image signal provided as an output by the image sensing means.
According to the aforementioned configuration, the instructing means is required to be provided only with a function of reflecting a ray, thus eliminating the need to incorporate a cell or electronic components. It is possible, for example, to adopt a configuration in which a reflecting member is provided at the tip of a shape similar to that of ordinary writing means such as a pen. It is thus possible to achieve a shape and a weight substantially identical with those of the ordinary writing means, and provide an advantage of easiness to use by an operator without any uncomfortable sense.
(2) In the coordinate input system of the invention as described in (1) above, a projection optical axis of the infrared projecting means does not cross the plane of the transmissive screen at right angles.
According to the configuration described above, the optical axis of the reflected ray from the back of the transmissive screen of the projected infrared ray from the infrared ray source, i.e., the maximum intensity direction has an angle with a direction at right angles to the plane of the screen. As a result, when the incident optical axis of the image sensing means is at right angles to the plane of the screen, the amount of incidence of the rear reflected infrared ray into the image sensing means becomes smaller, and this brings about an advantage of improving the S/N ratio (signal/noise ratio) of the detecting system.
(3) In the coordinate input system of the invention as described in (1) above, the optical axis of the image sensing means does not cross the plane of the transmissive screen at right angles.
According to the above-mentioned configuration, when the optical axes of the reflected ray from the screen back of the infrared ray source and the reflected ray from the screen back of the image ray for image display are at right angles to the plane of the screen, the amount of incidence of these reflected ray to the image sensing means becomes smaller, and this provides an advantage of an improved S/N ratio of the detecting system.
(4) In the coordinate input system of the invention as described in (1) above, the infrared projecting means comprises a plurality of infrared ray sources which project infrared ray to different areas of the back of the transmissive screen.
According to the aforementioned configuration, as compared with projection of an infrared ray to the back of the transmissive screen by the use of a single infrared ray source, it is possible to project the infrared ray uniformly over the entire back surface of the transmissive screen, thus providing an advantage of an improved S/N ratio of the detecting system.
(5) In the coordinate input system of the invention as described in (4) above, projection optical axes of the plurality of infrared ray sources do not cross the plane of the transmissive screen at right angles, and the angles of incidence of the projection optical axes of the plurality of infrared ray sources with the plane of the transmissive screen are different from each other.
According to the foregoing configuration, it is possible to make settings so that the incidence is diagonal as far as possible by using a different angle of incidence for each infrared ray source between the projection optical axes of the plurality of infrared ray sources and the plane of the transmissive screen. It is therefore possible to cause the maximum intensity distribution of the rear reflected ray from the transmissive screen of the ray projected from the infrared ray source to have a large angular difference to a direction at right angles to the transmissive screen. The optical axis of the image sensing means should on the other hand be at right angles in general to the plane of the transmissive screen so that the trapezoidal distortion is not generated in the sense image. As a result, the amount of incidence of the rear reflected ray on the transmissive screen of the infrared ray source can be reduced, and this results in an advantage of an improved S/N ratio of the detecting system.
(6) In the coordinate input system of the invention as described in (1) above, reflecting means of the indicating means comprises a reflective member having selectivity of infrared rays.
According to the configuration as described above, reflection of ray other than the infrared ray by the ray reflecting indicator can be inhibited. It is therefore possible to prevent reflection of image ray projected onto the transmissive screen not pertinent to the positional detection, thus permitting improvement of the S/N ratio of the detecting system.
(7) In the coordinate input system of the invention as described in (1) above, the reflecting means of the indicating means comprises an optical filter selectively allowing transmission of the infrared ray and an optical reflective member.
According to the aforementioned configuration, the advantage of inhibiting reflection of light other than the infrared ray from the light reflecting indicator and improving the S/N ratio of the detecting system can easily be achieved by means of a common optical components such as an optical glass filter and a mirror.
(8) In the coordinate input system of the invention as described in (1) above, the image sensing means has an optical filter which selectively allows transmission of the infrared ray within a wavelength range selectively reflected by the reflecting means of the indicating means.
According to the above-mentioned configuration, there is available an advantage of optically removing disturbance ray other than the infrared reflected ray from the ray reflecting indicator and improving the S/N ratio of the detecting system.
(9) In the coordinate input system of the invention as described in (1) above, the image information processing means has a subtracter which calculates a difference between first image information provided by the image sensing means upon turning on the infrared ray projecting means and second image information provided by the image sensing means upon turning off the infrared ray projecting means.
According to the configuration mentioned above, it is possible to eliminate pickup image information during turn-off of the infrared ray source, i.e., disturbance ray which is not an infrared reflected ray from the reflecting indicator, and extract only the infrared reflected ray from the reflecting indicator, thus providing an advantage of improving the S/N ratio of the detecting system.
(10) In the coordinate input system of the invention as described in (1) above, the infrared ray projecting means has infrared ray source synchronization turn-on control means, which synchronizes the timing of turn-on and turn-off of the infrared ray projecting means with the timing of frame switching between the first image information and the second image information.
According to the above-mentioned configuration, it is possible to obtain images of the image sensing means upon turn-on and turn-off of the infrared ray source in two consecutive frames (unit images). In order to obtain the difference between the image information provided as an output by the image sensing means upon turn-on of the infrared ray source and the image information upon turn-off thereof, it suffices to determine the difference between the two consecutive frames. This provides an advantage of permitting achievement of a higher-speed processing than in determination of the difference between two frames distant apart from each other, and further, another effect of inhibiting the capacity of the FIFO which is a frame memory necessary for differential processing to only one frame, the minimum capacity.
(11) In the coordinate input system of the invention as described in (1) above, the image ray projecting means has projected image frame synchronization control means which synchronizes the frame timing of the first image information and the second image information with the frame timing of a projected image of the image ray projecting means.
According to the above configuration, an image ray often presents a marked correlation between consecutive frames. It is therefore possible to remove almost completely the effect of rear reflection of the image ray by the transmissive screen, which becomes disturbance ray in positional coordinate detection by determining the difference between the image information provided as an output by the image sensing means upon turn-on of the infrared ray source and the image information provided as an output by the image sensing means upon turn-off thereof, thus permitting improvement of the S/N ratio of the detecting system.
(12) In the coordinate input system of the invention as described in (1) above, the image information processing means has disturbance discriminating means which compares a luminance level of the second image information provided as an output of the image sensing means upon turn-off of the infrared ray projecting means and a determination level.
According to the aforementioned configuration, when there is present disturbance of at least a certain value, it is possible to prevent an erroneous input by prohibiting coordinate detection.
(13) The display apparatus of the invention, which is provided with a transmissive screen forming an image from an image ray projected by image ray projecting means, comprises infrared ray projecting means which projects an infrared ray onto the back of the transmissive screen; image sensing means which picks up an image of an infrared ray reflected by instructing means provided with reflecting means in front of the transmissive screen, from the back of the transmissive screen; and image information processing means which determines coordinates on the transmissive screen as specified by the instructing means from an output image signal provided by the image sensing means.
According to the above-mentioned configuration, the indicating means is required to be provided only with a ray reflecting function, and it is not necessary to incorporate a cell or electronic components. It is therefore possible to adopt a configuration in which a reflecting member is provided at the tip of a shape similar to ordinary writing means such as a pen, thus permitting achievement of a shape and weight as in the ordinary writing means. In service, therefore, an operator can handle it without any feeling of uncomfortability. There is thus available a display apparatus having an easy-to-use coordinate input system enabling an effective and efficient presentation.